Balloon angioplasty is a well-known, standard treatment that restores blood flow in blocked arteries. Blockages occur when plaque accumulates in the walls of the blood vessels, forming lesions. In a conventional balloon angioplasty procedure, a catheter carrying an angioplasty balloon is inserted into the blood vessel along a guide wire to position the angioplasty balloon adjacent to a lesion. Progress of the guide wire may be tracked using fluoroscopy or x-rays. Inflating the angioplasty balloon compresses soft lesions on the wall of the vessel, thereby dilating the blood vessel and allowing blood to flow through a larger portion thereof. However, when plaque is hardened, or calcified, gentle compression may not be effective. In such cases, rapid expansion of the angioplasty balloon may occur when the calcified lesions break, so as to permit increasing the inner diameter of the blood vessel. Conventional balloon angioplasty techniques used to treat such calcified lesions may impart high stress that can damage vessel walls. Soft tissue damage often includes dissections or perforations that require placement of a stent to restore structural integrity to the blood vessel wall.
An improved electrohydraulic dilation technique has been used to treat calcified plaques using shock waves. Lithoplasty® technology is described in U.S. Pat. Nos. 8,956,371 and 8,888,788, assigned to Shockwave, Inc., of Fremont, Calif., both of which are incorporated by reference herein in their entireties. In this technique, electrodes are disposed inside the angioplasty balloon. The angioplasty balloon is inflated with a conductive fluid, for example, a saline solution, which will propagate shock waves, i.e., high energy pressure waves. When high voltage pulsed signals are applied to a bipolar emitter, i.e., a pair of emitter electrodes, a resulting plasma arc creates a rapidly expanding and collapsing gas bubble that emits a shock wave through the fluid. When a unipolar emitter is used, the high voltage signal arcs between a single emitter electrode and the fluid itself. Such shock waves have been shown to effectively break up, dislodge, or pulverize hardened plaques, thereby softening the lesion while preserving the integrity of the vessel walls. Following shock wave treatment, a conventional low-pressure angioplasty procedure can be used effectively to gently compress the softened lesions and dilate the blood vessel.